Digital watermarking is the process of embedding digital information into a data object to allow identification of the data object. The digital object is e.g. a data file, video file, audio file, a directory of files or streaming data. If the data object is copied, then the watermark is also carried in the copy. In visible watermarking, the information is visible in the picture or video. Typically, the information is text or a logo which identifies the owner of the media. In invisible watermarking, information is added as watermark data to the data object, but it cannot be perceived as such. Invisible watermarking is typically used in copyright protection systems, which are intended to prevent or deter unauthorized copying of data objects.
When a sequence of watermarks is added to a data object, this sequence of watermarks is called a fingerprint. An example of such fingerprint is described in U.S. Pat. No. 7,058,809 and European patent application 08100123.2. A fingerprint that is composed of a sequence of watermarks must be readily detectable in order to be useful. Extracting the watermark data forming the fingerprint from a data object is problematic if there are few clues as to where to find the individual watermark data or where the fingerprint starts or ends. Moreover, the watermark data in a sequence of identically-valued watermark data can be hard to count, and watermarking technologies that embed watermarks at variable locations—possibly with variable density—and with an unclear indication as to the precise location of the watermark data make the task even more difficult.
There is a need for an improved method and system for fingerprinting a data object and extracting a fingerprint from a data object to allow creation and verification of a fingerprinted data object.